Since I'm not really too familiar with electronics and stuff,
the only advice i could give, would be to concider the
"hands-on-method" again.. o)
Which means.. push the car and simply count the rotations..
I assume noone here knows the rotations per meter, you have
to find out for yourself, just as you did for the Dacia.
Btw, I know Dacia, my father once drove an orange
colored, the model I don't remember, but in east
germany, it was one of the better cars to drive, but my
dad had to sell it as he was short on money.. o)
By that time I was 5 or 6 years old.. nice to think of.. o)
Nevertheless, your project sounds very interesting,
I wouldn't mind you to post a few pictures when finished
or while still in progress.. o)
Btw, you could change the subject of this thread into:
"Wieviele Umdrehungen macht die Tachowelle pro km ?"
This should raise peoples attention..